Oil-in-water or water-in-oil emulsions often times utilize surfactants to decrease the interfacial tension between the oil and water to help prevent coalescence of water droplets of a water-in-oil emulsion or oil droplets of an oil-in-water emulsion. However, use of surfactants to help prevent coalescence has limitations to the extent to which coalescence of water droplets or oil droplets can be prevented. Surfactant methods use interfacial tension reduction as the means for inhibiting coalescence and stabilizing the emulsion.
Surfactant stabilized oil-in-water or water-in-oil emulsions have various uses including use in lubrication applications. However, the main drawback of an emulsion lubricant is its instability to shear and its shear-thinning characteristics. Lubrication applications involve contact between moving surfaces, and emulsion instability due to shear will result in emulsion break-up and subsequent loss of ability to function as a lubricant. In addition, in lubricant applications coalescence of water droplets of a water-in-oil emulsion or oil droplets of an oil-in-water emulsion may be exacerbated due to shear and shear thinning.
Interfacially active polymers may also stabilize the oil-water interface in emulsions and prevent coalescence by not only decreasing interfacial tension, but also increasing interfacial elasticity. Using polymers to inhibit coalescence may be superior and more robust than the use of surfactants. Suitable polymeric materials for increasing interfacial elasticity in emulsion compositions have been long sought after.
Accordingly, a need exists for emulsion compositions utilizing interfacially active polymers that have reduced tendency for coalescence, and also improved stability to shear and reduced shear-thinning when used in lubrication applications.